The goal of this proposal is to increase women's access to noninvasive radiotracer techniques that provide information about the metabolism and molecular biology of breast tumors. This goal will be accomplished by constructing low-cost dedicated breast imaging instruments that will improve the spatial resolution of positron-emitter techniques and reduce the dose of the examination to levels comparable with conventional mammography. Anticipated applications include the detection of cancer in patients whose mammograms are difficult to interpret, such as women with dense breasts or post-procedure scars. The device would facilitate neoadjuvant chemotherapy of locally advanced breast cancer by permitting noninvasive monitoring of therapeutic response. The proposed methodology consists of incorporating two high spatial resolution gamma-ray detector arrays within a conventional mammographic gantry (U.SA Patent 5,252,830 and 5,323,006). Phantom studies and computer simulations completed in Phase l suggest that small (subcentimeter) primary breast tumors will be confidently visualized in the proposed configuration at doses comparable to conventional mammography. PROPOSED COMMERCIAL APPLICATION: The largest market anticipated is in detecting cancer in women with difficult mammograms, such as women with dense fibroglandular tissue or scarring from prior biopsy. Potentially up to 30% of women could benefit from this device. The low-dose and low-cost features of the device will make the devices especially attractive for use in breast centers that do not have PET scanners.